Neutron diffraction study of quasi-one-dimensional lithium purple bronze: Possible mechanism for dimensional crossover

The crystallographic structure of quasi-one-dimensional lithium purple bronze (LPB) was investigated using neutron powder diffraction (NPD) at temperatures T in the range 5 $<T<$ 295 K. It has a monoclinic symmetry with space group P2₁/m, the lattice parameters at 295 K are a $=$ 12.7530(4) {}, b $=$ 5.5239(1) {}, c $=$ 9.4909(2) {}, and β $=$ 90.588(2)^∘. The sample stoichiometry was determined, through chemical analysis and refinement of the NPD data, to be Li0.924Mo₆O₁₇. The linear thermal expansion of the lattice parameters agrees with previously reported high-resolution dilatometry measurements. The bond-valence-sum method was applied to calculate the valence of each Mo ion as a function of T, which allows discussion of the mechanism by which charge is transferred between the double one-dimensional conducting chains.